LONDON - The share price of Antisoma plc fell by 40 percent Monday on news that a trial of a product "similar to" the company's lead product Theragyn, a radiolabeled HMFG1 murine monoclonal antibody, suggested there was a survival advantage favoring the control group.

Theragyn was licensed in November 1999 to Abbott Laboratories, which agreed to pay US$20 million to complete Phase III in ovarian cancer, and $40 million when the product achieved registration, which was expected to be in two years.

Antisoma, based in London, said it had decided to temporarily delay enrollment of any new patients to the Phase III pivotal trial, even though the findings of the unapproved study were inconsistent with its own Phase I/II Theragyn data, which has a 10-year follow-up analysis.

The unapproved study, by Steven Nicholson, a registrar at St George's Hospital, Tooting, London, was a poster presentation at the American Society of Clinical Oncology (ASCO) meeting in New Orleans.

CEO Glyn Edwards told BioWorld International, "We were alerted to the study by an investigator in the U.S. who saw the abstract on the [ASCO] web site. We did know he [Nicholson] was carrying out work with HMFG1, but we understood it was basic level research working with non-radiolabeled antibody to assess immune responses." In fact, Nicholson had treated ovarian cancer patients with HMFG1 labeled with the same radioisotope as Theragyn.

Nicholson obtained HMFG1 from the Imperial Cancer Research Fund, the charity from which Antisoma licensed the product. Edwards said that under the terms of the license the ICRF had the right to continue research with HMFG1. "If his [Nicholson's] research had been written up in a paper, he would have needed approval from the ICRF to publish, in which case we would have known about it. But because it was a poster he did not need approval."

Edwards said the Nicholson study was in a small group with only a short follow-up, but an inspection of the raw data hinted that there might have been a survival advantage for the control group. "It is not clear that survival increased in the control, but there is a hint of it so - not to denigrate Dr. Nicholson - we have to go back and make sure." For this reason he decided to stop Antisoma's Phase III until the data have been reviewed.

To date the Phase III has recruited 100 treated patients and 100 untreated patients over two years. "If the effect reported [in the Nicholson study] was correct we should have seen it by now," said Edwards. He stressed the overall safety of the Phase III trial is reviewed on a quarterly basis by an independent safety committee and that to date it has not raised any undue safety concerns.

Antisoma has asked the ICRF to organize an independent review of the data. Edwards said he had not contacted Nicholson directly because he did not want to be seen to be putting commercial pressure on him.

Antisoma informed Abbott as soon as it became aware of the study. "Of course they are not pleased because we were getting close to the end of recruitment, but they are putting a huge amount of effort into helping us sort this out," said Edwards.

Edwards said the company was also contacting investors to ensure they understood the nature of the problem. There will be cost implications of the delay, but Edwards said the main problem was the uncertainty the affair has generated. The company's share price fell 60.5 pence to 90 pence when news of the unapproved study was announced.

Edwards hopes the relationship with the ICRF will not be affected. "Dealing with charities and academics may be unpredictable, but it's a good thing to do."

This is the second time this month that a UK-quoted company has been knocked by an unexpected research report. Earlier in May shares in Scotia Pharmaceuticals plc fell by more than 25 percent when the Lancet published details of a safety study of its photodynamic therapy drug Foscan. Six volunteers in the study suffered serious burns at the site of the injection.